(i) Field of the Invention
The present invention relates to an apparatus for scrambling or descrambling in an FM multiplex broadcast, and more specifically, it relates to an apparatus for scrambling or descrambling by the use of data included in a prefix of communication data.
(ii) Description of the Prior Art
In an FM multiplex broadcast, the scrambling of a predetermined service before broadcasting has been investigated. An example of a service which is to be practically scrambled is road traffic information such as traffic jam information, traffic control and accident information provided by the Vehicle Information and Communication System Foundation (hereinafter referred to as "VICS").
For information transfer using FM multiplex broadcast, in addition to the VICS, there have been proposed, for example, services such as a pager and a DGPS (a differential global positioning system). Furthermore, also in Europe and America, the FM multiplex broadcast of a Japanese DARC (data radio channel) system is scheduled to be carried out. Additionally, in Europe and America, it has also been proposed to provide the services of the pager, various items of individual information such as stock prices and the DGPS information, using FM multiplex data. Since these services are basically provided by charged broadcasts, different scrambling is required to be applied to the services including free services which are not scrambled. Accordingly, in the FM multiplex broadcasts of one broadcasting station, the unscrambled broadcasts and the scrambled broadcasts (including plural kinds of scrambling) may exist together.
Thus, in the case where scrambling is applied or is not in applied to the broadcasts in one broadcasting station, they must be distinguished by some means. However, a concrete method for scramble control in such a case has not been proposed. Furthermore, in order to deal with this situation, various methods, such as the utilization of codes for denoting presence/absence of scrambling can be contrived. In such a case, however, various problems exist, and for example, specific mechanisms are necessary on both the transmitter and receiver sides.
Furthermore, if different PN codes for the scrambling are used for the scrambled broadcasts in accordance with the kinds of services (contents of the broadcasts), a user can distinguish the services. Thus, there has been a request that the different PN codes should be used in accordance with the kinds of services, but no concrete method for satisfying this request has been proposed.
The present applicant has disclosed a scrambling and descrambling method suitable for the FM multiplex broadcast in Japanese Patent Application No. 72740/1995. In this system, in the first place, key data included in one part of a data packet is determined on the transmitter side, and a scramble key is generated in accordance with the key data. Next, the scramble key is set to an initial value, and predetermined random numbers are generated. Furthermore, the PN code is created by nonlinear logic which is corrected and controlled by a data packet number. The data is scrambled by the PN code.
On the other hand, the key data or the like is extracted from the transmitted data which is received at the receiver side. In the same way as in the transmitter, the scramble key and the PN code are generated. The data within a predetermined range of the received data packet is descrambled. Accordingly, a suitable scrambling and descrambling processing for the FM multiplex broadcast can be carried out. However, in the previously proposed method, when broadcasts are scrambled and not scrambled at the same broadcasting station, a concrete method for scramble control has not been proposed.